Coal as a fuel is an abundant source of energy comprising mostly carbon and small percentages of hydrogen, sulfur and ash. When coal is burned to produce energy, the presence of sulfur and ash is generally undesirable. The sulfur and ash enter the atmosphere with the combustion products creating air pollution. The ash enters the air as particulates and the sulfur as noxious sulfur oxide gases.
Numerous processes have been proposed for upgrading coal by sulfur removal. A portion of the sulfur can be removed by existing technology, namely, "coal washing." This process removes pyritic sulfur which exists in natural coal in the form of separate particles ranging from the very small to large nuggets. The sulfur which cannot be removed by washing can only be removed by chemical processes. Generally speaking, there are three chemical coal desulfurization techniques disclosed in the prior art: (1) oxidation of sulfur in the coal to form soluble sulfates; (2) reduction of the sulfur to elemental sulfur in which form it can be vaporized or removed by organic solvents; and (3) reaction with hydrogen to form gaseous hydrogen sulfide.
For any sulfur removal process to be practical it must be adaptable to handling of large volumes of materials very economically. Hence, the reactants should be inexpensive and capable of being recycled and the apparatus should be rugged and simple. In the processes disclosed herein, the reactants are very common; namely, salt and hydrogen peroxide. Salt is available in many forms including brines pumped out of the ground and hydrogen peroxide is available in carload quantities. It is manufactured by several processes one of which includes the electrolysis of sulfate radicals, for example the electrolysis of sulfuric acid.